Cryo-applicator cross-section configuration

ABSTRACT

A configuration for a cryo-catheter which optimizes both the catheter&#39;s outer diameter and the size of the catheter&#39;s internal refrigerant flow path is described. Specifically, the inner dimensions of the cryo-catheter are configured to accommodate a pre-selected flow of refrigerant into the catheter&#39;s distal tip, and a return flow of refrigerant from the distal tip. The return flow is established in the void spaces between a refrigerant supply line and the inner wall of the catheter body. The available void space varies along the catheter length and depends on the presence/absence of various catheter accessories (i.e. pull wires, pressure tubes, etc.) which typically only extend through a portion of the catheter length. The disclosed configuration ensures that the cryo-catheter does not operate in a refrigerant limited condition, maintains the refrigerant as a liquid in the supply tube, and maintains the return line pressure at about 1 atmosphere.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/760,564 filed Jun. 8, 2007, now U.S. Pat. No. 8,377,050, the entiredisclosure of which is herein incorporated by reference.

FIELD OF THE INVENTION

The present invention pertains generally to systems and methods forcryoablating tissue. More particularly, the present invention pertainsto a configuration for a cryo-catheter having an active articulationsystem. The present invention is particularly, but not exclusively,useful as a configuration for a cryo-catheter which optimizes both thecatheter's outer diameter and the size of the catheter's internalrefrigerant flow path.

BACKGROUND OF THE INVENTION

Cryoablation has been successfully used in various medical procedures todestroy or deactivate selected tissues. In this context, it has beendetermined that cryoablation procedures can be particularly effectivefor curing heart arrhythmias, such as atrial fibrillation. It isbelieved that at least one-third of all atrial fibrillations originatenear the ostia of the pulmonary veins, and that the optimal treatmenttechnique is to treat these focal areas through the creation ofcircumferential lesions around the ostia of these veins.

Typically, to cryoablate selected tissue in and around the heart in anon-invasive procedure, a cryo-catheter is employed. In this regard,tissue in and around the heart is typically accessed from a peripheralartery such as the femoral or brachial artery. From the peripheralartery, the distal end of the catheter must navigate through the curvesand bends of a narrow and tortuous vascular tree to reach a targetedarea. In some cases, an introducer sheath is first inserted into thevasculature to establish a mechanical pathway to the treatment site.This allows the cryo-catheter to pass within the sheath from theperipheral artery to the treatment site. To be successful in locatingthe distal tip of a cryo-catheter at a treatment site, it is importantthat the catheter be flexible and have a relatively small outsidediameter. On the other hand, modern cryo-catheters typically require theincorporation of a number of sophisticated, internal catheter systemsthat must all somehow fit within the thin, low profile catheter. Thesesystems often include a first passageway to deliver a refrigerant froman extracorporeal location to the distal tip for expansion at the distaltip. A second passageway is also required to evacuate the expandedrefrigerant from the tip.

In addition to the internal systems described above, various monitoringsystems are often employed to measure tip temperature, tip pressure andelectrical signals from the heart (i.e. EKG signals). These systemsoften require pressure tubes, wires, sensors, electrode bands and othermonitoring components. Lastly, but perhaps equally important, moderncryo-catheters often include internal systems to articulate the distaltip of the catheter. These articulation systems can be used to steer thecryo-catheter during its journey through the vasculature and tomanipulate the distal tip of the catheter into contact with selectedtissue at a treatment site. For this purpose, these articulation systemstypically include pull wires, sheath springs, deflection supportstructures such as springs, and other peripheral components. Thus, allof these system components need to somehow fit within a low profilecryo-catheter while still leaving sufficient room along the entirelength of the catheter to deliver an ample quantity of refrigerant tothe distal tip and evacuate expanded refrigerant from the tip.

With the above in mind, for a typical medical procedure, cryoablationbegins at temperatures below approximately minus twenty degreesCentigrade (−20° C.). For the effective cryoablation of tissue, however,much colder temperatures are preferable. With this goal in mind, variousfluid refrigerants (e.g. nitrous oxide N₂O) have normal boiling pointtemperatures (i.e. the boiling point temperature at 1 atmospherepressure) as low as minus eighty eight degrees Centigrade (−88° C.). Animportant consideration in this regard is the fact that the temperatureat which a refrigerant boils is dependant on the pressure that therefrigerant is experiencing. Specifically, for a refrigerant such asnitrous oxide, the boiling temperature increases with increases inboiling pressure.

A low ablation temperature, however, is typically not sufficient toefficiently cryoablate tissue. Specifically, it is also necessary thatthere is a sufficient refrigeration potential to effectively freezetissue. In order for a system to both attain and maintain a suitablecryoablation temperature, while providing the necessary refrigerationpotential to effect cryoablation of tissue, several physical factorsneed to be considered.

In this regard, it is well known that when a fluid boils (i.e. changesfrom a liquid state to a gaseous state) a significant amount of heat istransferred to the fluid from its surroundings. With this in mind,consider a liquid that is not boiling, but which is under a condition ofpressure and temperature wherein effective evaporation of the liquidceases. A liquid in such condition is commonly referred to as being“fully saturated.” It will then happen, as the pressure on the saturatedliquid is reduced, the liquid tends to boil and extract heat from itssurroundings. Initially, the heat that is transferred to the fluid isgenerally referred to as latent heat. More specifically, this latentheat is the heat that is required to change a fluid from a liquid to agas, without any change in temperature. For some fluids, this latentheat transfer can be considerable. In this context, the refrigerationpotential is a measure of the capacity of a system to extract energyfrom its surroundings at a fixed temperature.

An important consideration for the design of any refrigeration system isthe fact that heat transfer is proportional to the difference intemperatures (ΔT) between the refrigerant and the body that is beingcooled. Importantly, heat transfer is also proportional to the amount ofsurface area of the body being cooled (A) that is in contact with therefrigerant. In addition to the above considerations (i.e. ΔT and A);when the refrigerant is a fluid, the refrigeration potential of therefrigerant fluid is also a function of its mass flow rate.Specifically, the faster a heat-exchanging fluid refrigerant can bereplaced (i.e. the higher its mass flow rate), the higher therefrigeration potential will be. This notion, however, has it limits.

As is well known, the mass flow rate of a fluid through a duct/tuberesults from a pressure differential on the fluid. More specifically, itcan be shown that as a pressure differential starts to increase on arefrigerant fluid in a system, the resultant increase in the mass flowrate of the fluid will also increase the refrigeration potential of thesystem. This increased flow rate, however, creates additional increasesin the return pressure (i.e. back pressure) that will result in adetrimental increase in the boiling point temperature of therefrigerant. Thus, for relatively low mass flow rates, increases in themass flow rate of the refrigerant will cause lower temperatures.Refrigerant flow in this range is said to be “refrigeration limited.” Onthe other hand, for relatively high mass flow rates, increases in themass flow rate actually cause the temperature of the refrigerant torise. Flow in this range is said to be “surface area limited.” Because acryo-catheter refrigeration system is least efficient at highertemperatures, operation under “refrigeration limited” conditions isgenerally avoided.

From the above discussion, it can be appreciated that a cryo-catheterrefrigeration system must be capable of performing three basicfunctions. First, it must deliver the refrigerant to the distal tip ofthe cryo-catheter in a liquid state so that the liquid can boil at thetip and absorb latent heat. Second, the system must evacuate theexpanded refrigerant and maintain the pressure where the refrigerantboils at a preselected pressure to ensure that the refrigerant boils ata low temperature. Lastly, the system must perform the first twofunctions at a sufficient refrigerant mass flow rate to generate thenecessary refrigeration potential to efficiently cryoablate tissue. Itis to be further appreciated that the satisfaction of these threerequirements is highly dependent on the size of the flow passages andexpansion chambers used to deliver the refrigerant to thecryo-catheter's distal tip and evacuate the expanded refrigerant fromthe tip.

In light of the above, it is an object of the present invention toprovide a cryo-catheter configuration which optimizes both thecatheter's outer diameter and the size of the catheter's internalrefrigerant flow path. It is another object of the present invention toprovide a cryo-catheter configuration that ensures that thecryo-catheter does not operate in a refrigerant limited condition. It isyet another object of the present invention to provide a configurationfor a cryo-catheter that cooperates to maintain a refrigerant in aliquid state as it transits through a supply tube and simultaneouslymaintains the pressure in a refrigerant return line at about 1atmosphere. Yet another object of the present invention is to provide acryo-catheter configuration which is easy to assemble, relatively simpleto implement, and comparatively cost effective.

SUMMARY OF THE INVENTION

The present invention is directed to a configuration for a cryo-catheterwhich optimizes both the catheter's outer diameter and the size of thecatheter's internal refrigerant flow path. In particular, the outerdiameter of the catheter is minimized to allow the catheter to beadvanced, percutaneously, through a patient's vasculature. On the otherhand, the inner dimensions of the cryo-catheter are configured toaccommodate a pre-selected flow of refrigerant into the catheter'sdistal tip, and importantly, a return flow of refrigerant from thedistal tip.

In greater structural detail, the cryo-catheter has a proximal end and adistal end and includes a tip at the distal end. The proximal end of thecryo-catheter is attached to a catheter handle. Between the handle andthe tip, the cryo-catheter includes a two-part catheter body having anarticulation segment and a braided segment. The braided segment extendsdistally from the catheter handle to the proximal end of thearticulation segment. For the cryo-catheter, the articulation segment ispositioned between the distal end of the braided segment and thecryo-catheter tip. Together, the braided segment and articulationsegment establish a central lumen which extends from the catheter handleto the catheter tip. With this cooperation of structure, the centrallumen has a first cross-sectional area in the articulation segment and asecond cross-sectional area in the braided segment.

To cool the cryo-catheter's distal tip, a two-part refrigerant supplyline is disposed in the central lumen. More specifically, the supplyline includes a high pressure supply tube and a flow restricting tube(e.g. capillary tube). Structurally, the capillary tube is attached toand extends from a distal end of the high pressure supply tube. In theoperation of the cryo-catheter, a regulated flow of liquid refrigerantis introduced into the proximal end of the high pressure supply tube.With this arrangement, the refrigerant traverses the supply tube, passesthrough the capillary tube and then outflows into an expansion chamberat the cryo-catheter's distal tip. Expanded refrigerant is thenexhausted from the chamber through a low pressure return line that isestablished in the void spaces between the outer wall of the supply lineand the inner wall of the catheter body. It is important to note thatthe exact nature and dimensions of these void spaces varies along thelength of the cryo-catheter. Specifically, at each location along thelength of the catheter, the available void space will depend on the sizeand extent of other catheter structures (i.e. accessories) that arepresent in the central lumen at that particular location. These catheteraccessories can include, but are not necessarily limited to, pull wires,sheath springs, sheath spring guide tubes, thermocouple wires, electrodewires and pressure measurement tubes. For the cryo-catheter, each ofthese accessories extends through some or all of the length of thecatheter.

The dimensions of the refrigerant flow paths are functionallysignificant and typically must be sized with several operationalobjectives in mind. Specifically, these dimensions control the pressuresand flow rates at critical points along the refrigerant flow path. Ingreater detail, the pressure within the high pressure supply tube mustbe sufficient to maintain the refrigerant in a liquid state throughoutthe length of the supply tube. On the other hand, the pressure in theexpansion chamber must be sufficiently low to allow for full refrigerantvaporization within the chamber. As a consequence, the capillary tubemust create the necessary pressure reduction between the high pressuresupply tube and the low pressure expansion chamber.

In addition to the requirements described above, the refrigerantpressures and flow path dimensions are generally designed to avoidoperation of the cryo-catheter in a refrigerant limited condition. Thiscondition is typically characterized as having a relatively low supplypressure for refrigerant entering the supply tube together with arelatively low return pressure. In the refrigerant limited condition,the catheter is typically unable to achieve the lowest possiblecryoablation temperature at the catheter's distal tip. Quantitatively,the expansion chamber is generally maintained at a pressure ofapproximately 1 atm. In addition, the accessories and fluid supply lineare arranged to leave a portion of a first cross-sectional area void inthe articulation segment and leave a portion of said secondcross-sectional area void in the braided segment. These voids establisha return path for a flow of gaseous refrigerant through the centrallumen. Preferably, the cryo-catheter is configured with the secondcross-sectional area void being greater than about thirty percent of thefirst cross-sectional area. As a consequence, the return path in thearticulation segment has a somewhat greater flow capacity than thereturn path in the braided segment. With this interactive cooperation ofstructure, refrigerant is maintained as a liquid in the high pressuresupply tube while maintaining the expansion chamber at a pressure ofabout 1 atm. to ensure that the cryo-catheter does not operate in arefrigerant limited condition.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of this invention, as well as the invention itself,both as to its structure and its operation, will be best understood fromthe accompanying drawings, taken in conjunction with the accompanyingdescription, in which similar reference characters refer to similarparts, and in which:

FIG. 1 is a perspective view of a cryo-catheter and catheter handle inaccordance with the present invention;

FIG. 2 is a side plan view of a distal portion of the cryo-cathetershown in FIG. 1, shown juxtaposed with a layout of internal catheteraccessories to illustrate the distal extent of each of the catheteraccessories;

FIG. 3 is a cross-sectional view of the cryo-catheter including internalaccessories as seen along line 3-3 in FIG. 2; and

FIG. 4 is a cross-sectional view of the cryo-catheter including internalaccessories as seen along line 4-4 in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially to FIG. 1, a system (generally designated 10) havinga cryo-catheter 12 and catheter handle 14 is shown. For the presentinvention, the system 10 can be used as part of a cryoablation apparatusto cryoablate a lesion in a body conduit of a patient (patient notshown). Although the system 10 is described herein for a catheter 12,those skilled in the pertinent art will appreciate that the systems andmethods described herein can be implemented with other applicators suchas a cryo-probe (not shown) that is configured to contact and ablateexposed tissue.

As indicated in FIG. 1, the cryo-catheter 12 includes an articulationsegment 16 that can be deflected using the catheter handle 14 intodifferent configurations and orientations. FIG. 1 further shows that thecryo-catheter 12 includes a braided segment 18 that extends distallyfrom the catheter handle 14 to the articulation segment 16. It can befurther seen that the cryo-catheter 12 includes a distal tip 20 that isattached to and extends distally from the articulation segment 16. Inuse, the distal tip 20 of the cryo-catheter 12 is typically insertedinto a patient through a peripheral artery, such as the femoral artery,and advanced through the patient's vasculature until the distal tip 20is positioned at a targeted location such as a location inside a heartchamber. Although the system 10 is capable of performing a cryoablationprocedure in an upper body vessel, such as a pulmonary vein, thoseskilled in the pertinent art will quickly recognize that the use of thesystem 10, as herein described, is not limited to use in any one type ofvessel, but, instead can be used in vascular conduits and other ductalsystems throughout the human body.

Referring now to FIG. 2, a distal portion of the cryo-catheter 12 isshown together with the distal portions of the various internal catheteraccessories. A sectional view of the internal catheter accessories thatare present in the articulation segment 16 is shown in FIG. 3 and asectional view of the internal catheter accessories that are present inthe braided segment 18 is shown in FIG. 4. As seen in FIG. 2, thecryo-catheter 12 includes the supply line 22 having a high pressuresupply tube 24 and a capillary tube 26. In a typical arrangement, thesupply tube 24 is sized to impart a negligible impedance to the flow ofrefrigerant through the supply tube 24. An exemplary supply tube 24 hasan inside diameter in the range of 0.017-0.022 inches, an outsidediameter in the range of 0.025-0.030 inches and a length of about 73inches. On the other hand, for the system 10, the capillary tube 26 istypically sized with a much greater impedance than the high pressuresupply tube 24, to thereby cause most of the supply line pressure dropto occur in the capillary tube 26. Functionally, this results in aconcentration of cooling power at the distal tip 20 of the catheter 12.Comparing FIGS. 3 and 4, it can be seen that the capillary tube 26 has amuch smaller inside diameter than the high pressure supply tube 24. Asbest seen in FIG. 2, the high pressure supply tube 24 terminates at adistal end 28 in the braided section 18. For the embodiment shown, thedistal end 28 is located several inches proximal to the articulationsegment 16. FIG. 2 also shows that the capillary tube 26 is attached tothe distal end 28 of the supply tube 24, extends therefrom through thearticulation segment 16, and terminates at a distal end 30 in the distaltip 20. An exemplary capillary tube 26 has an inside diameter in therange of 0.006-0.008 inches, an outside diameter in the range of0.016-0.018 inches and a length in the range of 4.9 inches to 9.8inches.

For the system 10 shown in FIG. 1, a refrigerant supply unit (not shown)is attached to the handle 14 to supply a refrigerant to the supply line22. At the refrigerant supply unit, various valves, pre-coolingcircuits, control systems and other components are connected to arefrigerant tank and configured to produce a regulated flow ofsub-cooled, liquid refrigerant which is then directed into the supplyline 22. In particular, a fluid refrigerant, such as Nitrous Oxide, isused that transitions from a liquid state to a gaseous state as itoutflows from the capillary tube 26 to cool the distal tip 20. Asuitable refrigerant supply unit for delivering a refrigerant in aliquid state to a supply line 22 for transition to a gaseous stateduring outflow from a capillary tube 26 is disclosed in co-pending,co-owned U.S. patent application Ser. No. 10/243,997, entitled “ARefrigeration Source for a Cryoablation Catheter” and filed on Sep. 12,2002. Co-pending U.S. patent application Ser. No. 10/243,997 is herebyincorporated by reference herein. In a typical application, NitrousOxide refrigerant is input into the proximal end of the high pressuresupply tube 24 at a pressure in the range of about 300 to 500 psi.

With reference to FIG. 2, refrigerant from the supply unit (not shown)traverses the supply tube 24, passes through the capillary tube 26 andthen outflows into an expansion chamber formed in the cryo-catheter'sdistal tip 20. Heat absorbed by the refrigerant during the liquid to gasphase transition (i.e. latent heat) cools the distal tip 20. Expandedrefrigerant is then exhausted from the expansion chamber through a lowpressure return line. As best seen in FIGS. 3 and 4, the low pressurereturn line is established in the void spaces 32 that are formed in thecentral catheter lumen. Typically, suction is applied to thelow-pressure return line via an extracorporeally located vacuum pump.Refrigerant suction pressures and flow path dimensions are generallydesigned to avoid operation of the cryo-catheter 12 in a refrigerantlimited condition. Quantitatively, the pressure in the distal portion ofthe return line is generally maintained in a range between 0.5 atm. and2 atm.

Comparing FIG. 3 with FIG. 4, it can be seen that the exact nature anddimensions of these void spaces 32 varies along the length of thecryo-catheter 12. Specifically, at each location along the length of thecryo-catheter 12, the available void space 32 will depend on the sizeand extent of the catheter accessories present in the central lumen atthat particular location. These catheter accessories will now bedescribed in greater detail.

With cross reference to FIGS. 2 and 3, an understanding of thearticulation segment 16 and the accessories that are present in thearticulation segment 16 can be obtained. As shown there, thearticulation segment 16 of the cryo-catheter 12 includes a deflectionstructure 34, which for the embodiment shown is a metal, helicallycoiled, spring. For the articulation segment 16, the deflectionstructure 34 is positioned in a flexible outer tube 36. In terms ofsize, the outer tube 36 has a catheter French size that is in the rangeof 8-10, allowing the catheter 12 to pass through a patient'svasculature. As detailed further below, the size of the outer tube 36 ispreferably as small as possible, subject to the condition that anadequately sized, low pressure return line is established.

With regard to the deflection structure 34, although a spring is shown,it is to be appreciated that other types of deflection structures can beused. For example, a deflection structure made of a thin walled,stainless steel material (e.g. 304 alloy) that has been cut with a laserto form transverse slits can be used. A more detailed description of thelaser cut deflection structure 34 can be found in co-pending, co-ownedU.S. patent application Ser. No. 10/774,665, filed Feb. 9, 2004, whichis hereby incorporated by reference in its entirety herein andco-pending, co-owned U.S. patent application Ser. No. 10/876,312 whichis also hereby incorporated by reference herein.

To deflect the articulation segment 16, the cryo-catheter 12 includes apull wire 38 having a distal end 40 that is attached to the distal tip20 and a proximal end (not shown) that is operationally attached to acontrol wheel (not shown) on the handle 14 (see FIG. 1). In use, thecontrol wheel can be activated to place the pull wire 38 in tension todeflect the distal tip 20. FIGS. 2 and 4 show that a central portion ofthe pull wire 38 is disposed in a metal, helically coiled, sheath spring42. The proximal end (not shown) of the sheath spring 42 is rigidlyattached to the handle 14 (see FIG. 1), extends therefrom and terminatesin a distal end 44 that is located approximately adjacent to the jointwhere the braided segment 18 attaches to the articulation segment 16.Functionally, the sheath spring 42 provides a compression force inresponse to the pull wire force, which in turn, allows for articulationof the distal tip 20.

An exemplary sheath spring has an inside diameter in the range of0.008-0.020 inches, an outside diameter in the range of 0.0115-0.025inches and is made of a wire having a diameter in the range of0.004-0.006 inches and an overall length of about 40 inches. It can befurther seen in FIGS. 2 and 4 that a portion on the sheath spring 42 isdisposed within a sheath spring guide tube 46. Typically, the sheathspring guide tube 46 extends from the handle 14 (see FIG. 1) andterminates at a distal end 48 that is located about one and one-halfinches proximal to the articulation segment 16. Functionally, the sheathspring guide tube 46 is used for support and to prevent gas leakage intothe sheath spring/pull wire assembly.

FIG. 2 also shows that the cryo-catheter 12 includes an EKG bandelectrode 50 and corresponding electrode wire 52. As shown, for thecryo-catheter 12, the electrode 50 is located near the distal end of thearticulation segment 16. From the electrode 50, the electrode wire 52extends proximally through the central lumen and extends within both thearticulation segment 16 and the braided segment 18 (see also FIGS. 3 and4). From the braided segment 18, the electrode wire 52 typically passesthrough the handle 14 (see FIG. 1) to an EKG monitor (not shown). Forthe cryo-catheter 12, the electrode wire 52 is typically a Nickel wirehaving an outside diameter in the range of 0.008-0.011 inches that isdisposed in a polyimide sleeve 54. The use of a sleeve 54 over the wire52 prevents electrical shorts with other components of the cryo-catheter12. FIGS. 2 and 3 also show that a thermocouple wire set 56 is disposedin the central lumen of the cryo-catheter 12 to measure a distal tip 20temperature. As shown, the thermocouple wire set 56 extends through boththe braided segment 18 and articulation segment 16 and terminates in adistal end 58 that is located in the distal tip 20. For thecryo-catheter 12, the thermocouple wire set 56 extends through thehandle 14 to a temperature monitor (not shown).

As best seen in FIGS. 2 and 4, the cryo-catheter 12 includes a pressuremeasurement tube 60 that is disposed in the central lumen of the braidedsegment 18. As shown, the pressure measurement tube 60 has a distal end62 that is positioned at a location proximal to the joint where thebraided segment 18 attaches to the articulation segment 16 (i.e. about 1inch proximal to the articulation segment 16). From its distal end 62,the pressure measurement tube 60 extends proximally through the handle14 (see FIG. 1) to a pressure monitor (not shown) which measures apressure at the proximal end of the pressure measurement tube 60.Together, the pressure measurement tube 60 and pressure monitorcooperate to provide an estimate of the pressure in the low pressurereturn line near the distal tip 20. An exemplary pressure measurementtube 60 has an inside diameter in the range of 0.017-0.022 inches, anoutside diameter in the range of 0.025-0.030 inches and a length ofabout 73 inches.

As indicated above, an important functional consideration for thecryo-catheter 12 is its ability to transfer a fluid refrigerant to thecatheter's distal tip 20 as a liquid, and to then exhaust therefrigerant back through both the articulation segment 16 and thebraided segment 18, as a gas. As also indicated above, however, theoutside dimensions of the cryo-catheter 12 are constrained by anatomicalrequirements. Operationally, these outside dimensions necessarily impacton the economies that can be obtained for fluid refrigerant flow insidethe cryo-catheter 12. With these constraints in mind, the consequentrequirement is that there be the maximum possible void space within thecryo-catheter 12 for exhausting the gas refrigerant from thecryo-catheter 12. Both the articulation segment 16 and the braidedsegment 18 are involved here.

Table A, shown below, provides exemplary maximum and minimum dimensionsfor specified components that may be incorporated into the cryo-catheter12 and positioned in the articulation segment 16. Table A is, perhaps,best appreciated by cross-referencing it with FIG. 3.

TABLE A Min Meas. Max Meas. Deflection Structure (34) Inner Diameter 7.8E−02 7.900E−02 in. Area 4.778E−03 4.902E−03 sq. in. Capillary Tube(26) Outer Diameter 1.600E−02 1.800E−02 in. Area 2.011E−04 2.545E−04 sq.in. Pull Wire (38) Outer Diameter  1.0E−02 1.100E−02 in. Area 7.854E−059.503E−05 sq. in. Electrode Wire (52) Outer Diameter 8.000E−03 1.100E−02in. Area 5.027E−05 9.503E−05 sq. in. Thermocouple Wire Set (56) OuterDiameter 7.000E−03 8.000E−03 in. Area 3.848E−05 5.027E−05 sq. in. VoidSpace Area (32) 4.410E−03 4.407E−03 sq. in.Using the numbers provided above, it is easily determined that the voidspace within the articulation segment 16 will be in a range of about89.4% to about 91.4% of the space available inside the deflectionstructure 34 of articulation segment 16.

Similar to Table A, Table B shown below, provides exemplary maximum andminimum dimensions for specified components that may be positioned inthe braided segment 18. Table B is, perhaps, best appreciated bycross-referencing it with FIG. 4.

TABLE B Min Meas. Max Meas. Catheter Cross Section Inner Diameter9.900E−02 9.950E−02 in. Area 7.698E−03 7.776E−03 sq. in. Supply Tube(24) Outer Diameter 2.500E−02 3.000E−02 in. Area 4.909E−04 7.069E−04 sq.in. Spring Sheath (42) Outer Diameter 1.150E−02 2.500E−02 in. Area1.039E−04 4.909E−04 sq. in. Pressure Measuring Tube (60) Outer Diameter2.500E−02 3.000E−02 in. Area 4.909E−04 7.069E−04 sq. in. Electrode Wire(52) Outer Diameter 8.000E−03 1.100E−02 in. Area 5.027E−05 9.503E−05 sq.in. Thermocouple Wire Set (56) Outer Diameter 7.000E−03 8.000E−03 in.Area 3.848E−05 5.027E−05 sq. in. Void Space Area (32) 6.524E−035.726E−03 sq. in.Using the numbers provided above, it is easily determined that the voidspace within the braided segment 18 will be in a range of about 73.0% toabout 84.2% of the space available inside the braided segment 18.

An important observation to be made from Tables A and B is the factthat, although the percentage of void space in articulation segment 16is greater than the percentage of void space in the braided segment 18,the actual void space in the braided segment 18 is greater. As indicatedabove, this relationship is established to ensure maximum operationalefficiency.

While the particular Cryo-applicator Cross-Section Configuration andcorresponding methods of use as herein shown and disclosed in detail arefully capable of obtaining the objects and providing the advantagesherein before stated, it is to be understood that they are merelyillustrative of the presently preferred embodiments of the invention andthat no limitations are intended to the details of construction ordesign herein shown other than as described in the appended claims.

What is claimed is:
 1. A configuration for cooling a medical devicehaving a proximal end and a distal end, the configuration comprising: acatheter shaft including a distal segment having a distal end and aproximal end, a tip at the distal end of said distal segment, and aproximal segment attached to said distal segment, wherein said proximalsegment and said distal segment define a central lumen extending throughat least a portion of said catheter shaft, wherein said central lumenhas a first cross-sectional area in said distal segment and a secondcross-sectional area in said proximal segment, wherein the secondcross-sectional area of the proximal segment is greater the firstcross-sectional area; and a fluid supply line for transferring a coolantthrough said central lumen of said proximal segment and said distalsegment to said tip; wherein a return path for a flow of coolant isdefined in said central lumen by a void created between said fluidsupply line and said catheter shaft, and further wherein the return pathincludes a first void space in the proximal segment that is at leastabout 30% greater in cross-sectional area than a second void space inthe distal segment.
 2. The configuration of claim 1, further comprisingone or more accessory positioned in said central lumen.
 3. Theconfiguration of claim 2, wherein the accessory positioned in saidcentral lumen includes a steering element.
 4. The configuration of claim2, wherein the accessory positioned in said central lumen includes athermocouple wire.
 5. The configuration of claim 2, wherein theaccessory positioned in said central lumen includes an electrode wire.6. A configuration for cooling a catheter shaft having a proximal endand a distal end, the configuration comprising: a tip at the distal endof said catheter; a handle at the proximal end of said catheter; anarticulation segment attached to said tip; a proximal segment attachedto said articulation segment and to said handle, wherein the proximalsegment and the articulation segment define a central lumen extendingbetween said handle and said tip, and wherein said central lumen has afirst cross-sectional area in said articulation segment and a secondcross-sectional area in said proximal segment, wherein said secondcross-sectional area is greater than said first cross-sectional area; afluid supply line for transferring a coolant through said central lumenof said proximal segment and said articulation segment to said tip; areturn path for a flow of coolant defined in said central lumen by voidspace created between said fluid supply line and said catheter shaft,wherein the return path includes a first void space in the proximalsegment that is at least about 30% greater in cross-sectional area thana second void space in the articulation segment; and at least oneaccessory positioned in said central lumen spaced from each of the fluidsupply line and the catheter shaft.
 7. The configuration of claim 6,wherein said at least one accessory includes a pull wire.
 8. Theconfiguration of claim 6, wherein said at least one accessory includes athermocouple wire.
 9. The configuration of claim 6, wherein said atleast one accessory includes an electrode wire.
 10. The configuration ofclaim 6, wherein said at least one accessory includes a pressure sensor.11. The configuration of claim 6, wherein said fluid supply meansincludes a hollow supply tube and a capillary tube.
 12. A cooledcatheter having a proximal end and a distal end, the cathetercomprising: a tip at the distal end of said catheter; a handle at theproximal end of said catheter; an articulation segment attached to saidtip; a proximal segment attached to said articulation segment and tosaid handle, said articulation segment and said proximal segmentdefining a central lumen extending between said handle and said tip, andwherein said central lumen has a first cross-sectional area in saidarticulation segment and a second cross-sectional area in said proximalsegment, wherein said second cross-sectional area is greater than saidfirst cross-sectional area; a fluid supply configured to provide acoolant through said central lumen to said tip; a return path for a flowof coolant defined in said central lumen by a void space created betweensaid fluid supply and a wall of the catheter, wherein the return pathincludes a first void space in the proximal segment that is greater incross-sectional area than a second void space in the articulationsegment; and at least one accessory positioned in said central lumen andspaced from each of the fluid supply and catheter shaft
 13. The catheterof claim 12 wherein said at least one accessory includes a pull wire.14. The catheter of claim 12 wherein said at least one accessoryincludes a thermocouple wire.
 15. The catheter of claim 12 wherein saidat least one accessory includes an electrode wire.
 16. The catheter ofclaim 12 wherein said at least one accessory includes a pull wire, athermocouple wire, and an electrode wire.